Artificial dielectric material for controlling antennae patterns

ABSTRACT

A loaded dielectric material for use in controlling antennae patterns has sheets carrying small discrete conductors incorporated into a dielectric material. The sheets may be incorporated as walls in cellular construction material to give a light weight high strength dielectric material suitable for use as part of an antenna in helicopter rotor blades and rotodomes.

United States Patent Cary et a1. 1 1 May 27, 1975 [54] ARTIFICIAL DIELECTRIC MATERIAL FOR 2,978,702 4/1961 Pakan 343/753 CONTROLLING ANTENNAE PATTERNS 3,137,000 6/1964 Fuller i 4 343/909 3,329,958 7/1967 Anderson... 343/753 1 Inventors: Rex Henry J y; Alexander 3.390.393 6/1968 Upton 4 a n 343/708 McKay Munro, both of Malvern, 3,430,248 2/1969 Lightbowne 7. 343/911 R England 3,478,353 11/1969 Adams 343 703 3,633,206 l/1972 McMillanmv... r r H 343/909 [73] Assignee: British Secretary of State for 3,754 271 8/1973 Epis 343/909 Defense, Whitehall, London, 3366,56] 10/1973 Johnson 343/705 England [22] Filed: July 31, 1973 Primary ExaminerEli Lieberman Appl. No.: 384,351

Foreign Application Priority Data Aug. 4, 1972 United Kingdom 36445/72 US. Cl. 343/708; 343/753; 343/872; 343/91 1 R int. Cl.. H01q 1/28 Field of Search 343/753, 909, 911 R, 755, 343/754, 708, 872

References Cited UNITED STATES PATENTS 6/1958 McMillan 343/754 Attorney, Agent, or FirmElliott l. Pollock [57] ABSTRACT 7 Claims, 14 Drawing Figures Patented May 27, 1975 3 Sheets-Shut 1 Patented May 27, 1975 3 Sheets-Sheet 3 FIG. 5.

FIG. 50.

Patented May 27, 1975 3,886,558

3 Sheets-Shoot 5 FIG. 8.

ARTIFICIAL DIELECTRIC MATERIAL FOR CONTROLLING ANTENNAE PATTERNS BACKGROUND OF THE INVENTION This invention relates to an improved dielectric material for controlling antennae patterns which may inelude imparting super gain properties, by combining artificial dielectrics with aircraft structure material which while maintaining their mechanical strength eases the installation problems and involves a minimum weight penalty.

Antennae on aircraft may be housed in or supported external to the aircraft. There are cases where the aerial pattern may be required to be controlled, possibly to include super gain properties, by adding tuned elements for example Yagi type antennas which introduce structural support problems. The controlling of antenna patterns by normal dielectric lenses is not preferred due to the heavy weight penalty they usually incur. It is known that light weight artificial dielectrics can be produced by mixing metal flake, disc or spheres in a low dielectric matrix. However such materials produced in the past have tended to result in materials possessing excessive electrical loss, lack of control of permittivity or a material which does not possess the required mechanical properties, particularly extreme light weight, for the aircraft application.

SUMMARY OF THE INVENTION According to this invention a loaded dielectric material for controlling antennae pattern includes thin sheets of a dielectric material carrying numerous discrete electrical conductors spaced in a dielectric material to give required permittivity.

The conductor may be formed by printing, photo etching, vapour deposition, spraying etc of metal or other suitable conductor on thin plastic sheet. Spacing between these thin sheets may be varied as may the density and dimension of conductors on successive sheets.

Preferably the thin sheets carrying conductors are incorporated in a material of cellular form such as honeycomb, fluted or similar shape either by including the conductor on its cell walls or within its cell without impairing the structural strength.

The loading can be controlled to produce the desired permittivity, to a high degree of accuracy, necessary to control the antenna pattern while avoiding any measurable increase in electrical loss.

A preferred aircraft structural material employs a sandwich type of construction using the loaded cellular material as a core to give a light weight yet strong material. By suitable arrangement of the thin sheets carrying conductors an antenna having super gain properties may be made using the preferred sandwich type construction to give a high strength light weight antenna.

Forms of the invention, given by way of example only, are illustrated in the accompanying drawings in which:

FIGS. Ia, lb and 1c show the loading of thin sheets of dielectric materials with fine discrete metallic conductors of various shapes;

FIGS. 2, 2a, 3, and 3a show examples of loading cellular materials with the loaded sheets shown at FIGS. la, lb and 16;

FIG. 4 shows an antenna mounted in the trailing edge of a helicopter rotor blade;

FIG. 5 shows typical radiation pattern;

FIG. 5a shows assymmetrical radiation pattern;

FIG. 6 is a diagrammatic view showing a rotodome mounted on an aircraft;

FIG. 7 is a plan view of a rotodome incorporating a line of radiating sources near its central plane.

FIG. 7a shows an alternative arrangement for the radiators to that of FIG. 7; and

FIG. 8 is an enlarged sectional part view of rotodome shown at FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. la shows a sheet I of extremely thin and light weight dielectric material carrying a number of cross shaped conductors 2 formed by photo etching, vapour deposition, printing, spraying or any other suitable process. The conductors are electrically short, typically about one eighth of the wavelength of the operating frequency.

FIG. 1b shows unidirectional thin conductors 4 on dielectric sheet 3.

FIG. 10 shows thin circular conducting discs 6 on a dielectric sheet 5.

The spacing and dimensions of the conductors 2, 4 and 6 can be varied to give the desired permittivity.

FIG. 2 shows sheets I of FIG. 1a incorporated into a fluted structure 7 with sheets I, carrying the conductors 2, at required spacing. These spacings may be uniform or varied to give desired permittivities.

FIG. 2a shows an alternative fluted structure 7 in which sheets 1 are inserted into the elongated tubular cells 8 of the fluted material 7, the size and number of the conductors in the individual cells being chosen to give the correct permittivity.

FIG. 3 shows the sheets 1 incorporated into a honeycomb structure 9 formed of hexagonally shaped cellular honeycomb material 10 with sheets I carrying the conductors 2 at required spacing.

FIG. 3a shows an alternative honeycomb structure 9 in which the material 10 forming the walls of the Iongated tubular cells is replaced by sheets 1 at desired spacings.

An alternative arrangement (not shown) for the loading of the honeycomb material is similar to that used in FIG. 2a where sections of sheets 1 are inserted into the cells of the honeycomb 10. The size and number of conductors inserted is chosen to give the desired permittivity. In all of above arrangements material 1 may be replaced by either material 3 or 5 shown at FIG. lb and 10 respectively with alternative forms of conductors 4, 6.

FIG. 4 shows an antenna 13 built into the trainling edge of a helicopter rotor blade 12. Inside rotor blade 12 is a typical waveguide 11 provided with inclined slots through which the antenna 13 emits and receives radio waves. In front of the waveguide is a wedge shaped, tubular cellular type, low density dielectric core 14. The dielectric properties of this core 14 are modified to give the desired permittivity required to give the required beam shape by the use of either sheets I, 3, or 5 shown in FIGS. la, lb or 1c respectively spaced to produce a material as or similar to that shown at FIGS. 2, 2a, 3 or 3a. In order to provide a sound mechanical structure, cellular core 14 is enclosed by high tensile dielectric skins 15 to form a sandwich structure with the tubular cells in core 14 having their opposing ends closed by skins 15. These skins 15 usually require to be matched to ensure that the beam shape and gain are preserved. for example by incorporating electrically long thin wire within the skin.

FIG. 5 shows a typical symmetrical radiation diagram achieved by the antenna of the present invention.

FIG. 5a shows an asymmetric radiation pattern which may be obtained by assymmetric loading of the core 14, and, or positioning of the wave guide 11. Metallic surfaces local to the waveguide 11 may also be used.

The antenna 13 may be given super gain properties by suitable arrangement of the sheets 1 carrying the conductors 2 in the core 14 and tapering of the core as shown.

An example of an antenna built into a helicopter rotor blade in accordance with the present invention had the following dimension and characteristics: width (from waveguide 11 the trailing edge) of 250 mm; length (measured along rotor blade) of 260 mm, waveguide 11 slot pitch of 23 mm, sheets 1 spaced 20 mm apart; conductors 2 arranged on sheets 1 at a staggered pitch of 5 mm with a conductor length of 4.5 mm and section of 0.5 X 0.05 mm; the core 14 made from Nomex Honeycomb of density 2 lb/cu.ft. with 4.7 mm hexagonal cells; and skins 15 of 0.75 mm thick glass fibre laminate loaded with 0.06 mm diameter wire arranged at a 1.2 mm pitch. When operated at 9.4 to 9.8 GHz the antenna produced a 23 beam width at 3dB 1% power), with side lobes better than 13 dB in plan orthogonal to the waveguide 11 direction.

The dielectric core material shown in FIG. 2 and 3 can be advantageously used in a rotodome 16, FIG. 6, mounted on aircraft 17 on bearings so that it can be rotated about a vertical axis during flight. The rotodome 16 is approximately elliptical in cross-section and symmetrical about a vertical axis. Inside the rotodome 16 is an antenna system for transmitting and receiving radar frequency waves as the rotodome is rotated.

As shown in FIGS. 7 and 8, a radiating array 18 is mounted in the rotodome 16. In front of the radiating array 18 i.e. between it and the edge of rotodome 16 is a taper shaped (in cross section) core 19 of cellular dielectric material incorporating the artificially loaded material shown in FIGS. 2, 2a, 3 or 3a with the conducting elements 2, 4, or 6 arranged to provide the required beam profile.

In FIG. 7 the radiating array 18 is arranged near the central plane of the rotodome 16 whereas in FIG. 7a, the radiating array 20 is displaced from this plane.

A futher advantageous feature of these examples of the use of these light weight artificial dielectric material is that the bandwidths of the resulting antennae are much wider than with tuned element or Yagi Type arrays. The patterns can be also arranged by control of the artificial dielectric loading to give low side lobes and better repeatability.

What we claim is:

1. An antenna comprising means for transmitting and receiving electromagnetic waves, a shaped core of cellular dielectric material fixed between two high tensile skins of dielectric material, said shaped core being disposed adjacent said transmitting and receiving means, the cellular material of said core comprising a plurality of continuous sheets of thin dielectric material fixed together to form a plurality of elongated, hollow tubular, cells the walls of which constitute said sheets, the walls of said cells being disposed transverse to the direction of transmission and reception of the electromagnetic waves whereby said waves travel through the side walls of said cells, the longitudinal axes of said tubular cells being parallel to one another, the lengths of different ones of said cells differing from one another to define the shape of said core, the opposing ends of the tubular cells being closed by said high tensile skins which are curved smoothly to conform to the relative positions of the ends of said different length cells thereby to provide a core and skin structure which is itself capable of withstanding structural loads, and the surface of at least some of said dielectric sheets carrying numerous discrete electrical conductors of elongated configuration there on operative to modify the dielectric properties of the shaped core thereby to control the antenna radiation pattern.

2. The antenna of claim 1 wherein said elongated discrete electrical conductors are disposed on said surfaces in a plurality of cross shaped configurations spaced from one another.

3. The antenna of claim 1 wherein said elongated discrete electrical conductors are disposed on said sheet surfaces in unidirectional spaced relation to one another.

4. The antenna of claim 1 wherein said shaped core comprises a unitary portion of a helicopter rotor blade.

5. The antenna of claim 4 wherein said means for transmitting and receiving electromagnetic waves comprises a waveguide disposed within the helicopter rotor blade.

6. The antenna of claim 1 wherein said shaped core comprises a unitary portion of a rotodome arranged for mounting on an aircraft.

7. The antenna of claim 1 wherein said transmitting and receiving means constitutes an elongated waveguide, the axis of said waveguide being transverse to the longitudinal axes of the tubular cells in said shaped core. 

1. An antenna comprising means for transmitting and receiving electromagnetic waves, a shaped core of cellular dielectric material fixed between two high tensile skins of dielectric material, said shaped core being disposed adjacent said transmitting and receiving means, the cellular material of said core comprising a plurality of continuous sheets of thin dielectric material fixed together to form a plurality of elongated, hollow tubular, cells the walls of which constitute said sheets, the walls of said cells being disposed transverse to the direction of transmission and reception of the electromagnetic waves whereby said waves travel through the side walls of said cells, the longitudinal axes of said tubular cells being parallel to one another, the lengths of different ones of said cells differing from one another to define the shape of said core, the opposing ends of the tubular cells being closed by said high tensile skins which are curved smoothly to conform to the relative positions of the ends of said different length cells thereby to provide a core and skin structure which is itself capable of withstanding structural loads, and the surface of at least some of said dielectric sheets carrying numerous discrete electrical conductors of elongated configuration there on operative to modify the dielectrIc properties of the shaped core thereby to control the antenna radiation pattern.
 2. The antenna of claim 1 wherein said elongated discrete electrical conductors are disposed on said surfaces in a plurality of cross shaped configurations spaced from one another.
 3. The antenna of claim 1 wherein said elongated discrete electrical conductors are disposed on said sheet surfaces in unidirectional spaced relation to one another.
 4. The antenna of claim 1 wherein said shaped core comprises a unitary portion of a helicopter rotor blade.
 5. The antenna of claim 4 wherein said means for transmitting and receiving electromagnetic waves comprises a waveguide disposed within the helicopter rotor blade.
 6. The antenna of claim 1 wherein said shaped core comprises a unitary portion of a rotodome arranged for mounting on an aircraft.
 7. The antenna of claim 1 wherein said transmitting and receiving means constitutes an elongated waveguide, the axis of said waveguide being transverse to the longitudinal axes of the tubular cells in said shaped core. 